你最喜欢的C#扩展方法是什么？（codeplex.com/extensionoverflow）

希望能够提供Unix时间戳和ISO 8601格式的日期和时间。这在网站和REST服务中被广泛使用。

我在我的Facebook库中使用它。您可以在http://github.com/prabirshrestha/FacebookSharp/blob/master/src/FacebookSharp.Core/FacebookUtils/DateUtils.cs找到源代码。

private static readonly DateTime EPOCH = DateTime.SpecifyKind(new DateTime(1970, 1, 1, 0, 0, 0, 0),DateTimeKind.Utc);

public static DateTime FromUnixTimestamp(long timestamp)
{
    return EPOCH.AddSeconds(timestamp);
}

public static long ToUnixTimestamp(DateTime date)
{
    TimeSpan diff = date.ToUniversalTime() - EPOCH;
    return (long)diff.TotalSeconds;
}

public static DateTime FromIso8601FormattedDateTime(string iso8601DateTime){
    return DateTime.ParseExact(iso8601DateTime, "o", System.Globalization.CultureInfo.InvariantCulture);
}

public static string ToIso8601FormattedDateTime(DateTime dateTime)
{
    return dateTime.ToString("o");
}

欢迎在codeplex项目中使用。

这是我唯一编写并经常使用的扩展。它使得使用System.Net.Mail发送电子邮件更加容易。

public static class MailExtension
{
    // GetEmailCreditial(out strServer) gets credentials from an XML file
    public static void Send(this MailMessage email)
    {
        string strServer = String.Empty;
        NetworkCredential credentials = GetEmailCreditial(out strServer);
        SmtpClient client = new SmtpClient(strServer) { Credentials = credentials };
        client.Send(email);
    }

    public static void Send(this IEnumerable<MailMessage> emails)
    {
        string strServer = String.Empty;
        NetworkCredential credentials = GetEmailCreditial(out strServer);
        SmtpClient client = new SmtpClient(strServer) { Credentials = credentials };
        foreach (MailMessage email in emails)
            client.Send(email);
    }
}

// Example of use: 
new MailMessage("info@myDomain.com","you@gmail.com","This is an important Subject", "Body goes here").Send();
//Assume email1,email2,email3 are MailMessage objects
new List<MailMessage>(){email1, email2, email}.Send();

http://www.codeplex.com/linqext/

我在我的Web项目中使用这些，主要与MVC一起使用。我编写了几个用于ViewData和TempData的代码片段。

/// <summary>
/// Checks the Request.QueryString for the specified value and returns it, if none 
/// is found then the default value is returned instead
/// </summary>
public static T QueryValue<T>(this HtmlHelper helper, string param, T defaultValue) {
    object value = HttpContext.Current.Request.QueryString[param] as object;
    if (value == null) { return defaultValue; }
    try {
        return (T)Convert.ChangeType(value, typeof(T));
    } catch (Exception) {
        return defaultValue;
    }
}

那么我可以翻译类似这样的内容...

这样我就可以写出类似的东西...

<% if (Html.QueryValue("login", false)) { %>
    <div>Welcome Back!</div>

<% } else { %>
    <%-- Render the control or something --%>

<% } %>

在字符串类上的子字符串方法对我来说一直感觉不够充分。通常，当你做一个子字符串时，你知道你想要从哪里开始的字符和你想要结束的字符。因此，我一直觉得必须指定长度作为第二个参数是愚蠢的。因此，我编写了自己的扩展方法。一个是接受startIndex和endIndex的方法。还有一个，它接受startText（字符串）和endText（字符串），这样你就可以只指定从哪里开始子字符串以及在哪里结束它的文本。
注意：我不能像.NET中那样命名方法为Substring，因为我的第一个重载采用了与.NET重载之一相同的参数类型。因此，我将它们命名为Subsetstring。请随意添加到CodePlex...

public static class StringExtensions
{
    /// <summary>
    /// Returns a Subset string starting at the specified start index and ending and the specified end
    /// index.
    /// </summary>
    /// <param name="s">The string to retrieve the subset from.</param>
    /// <param name="startIndex">The specified start index for the subset.</param>
    /// <param name="endIndex">The specified end index for the subset.</param>
    /// <returns>A Subset string starting at the specified start index and ending and the specified end
    /// index.</returns>
    public static string Subsetstring(this string s, int startIndex, int endIndex)
    {
        if (startIndex > endIndex)
        {
            throw new InvalidOperationException("End Index must be after Start Index.");
        }

        if (startIndex < 0)
        {
            throw new InvalidOperationException("Start Index must be a positive number.");
        }

        if(endIndex <0)
        {
            throw new InvalidOperationException("End Index must be a positive number.");
        }

        return s.Substring(startIndex, (endIndex - startIndex));
    }

    /// <summary>
    /// Finds the specified Start Text and the End Text in this string instance, and returns a string
    /// containing all the text starting from startText, to the begining of endText. (endText is not
    /// included.)
    /// </summary>
    /// <param name="s">The string to retrieve the subset from.</param>
    /// <param name="startText">The Start Text to begin the Subset from.</param>
    /// <param name="endText">The End Text to where the Subset goes to.</param>
    /// <param name="ignoreCase">Whether or not to ignore case when comparing startText/endText to the string.</param>
    /// <returns>A string containing all the text starting from startText, to the begining of endText.</returns>
    public static string Subsetstring(this string s, string startText, string endText, bool ignoreCase)
    {
        if (string.IsNullOrEmpty(startText) || string.IsNullOrEmpty(endText))
        {
            throw new ArgumentException("Start Text and End Text cannot be empty.");
        }
        string temp = s;
        if (ignoreCase)
        {
            temp = s.ToUpperInvariant();
            startText = startText.ToUpperInvariant();
            endText = endText.ToUpperInvariant();
        }
        int start = temp.IndexOf(startText);
        int end = temp.IndexOf(endText, start);
        return Subsetstring(s, start, end);
    }
}

使用方法：

string s = "This is a tester for my cool extension method!!";
       s = s.Subsetstring("tester", "cool",true);

输出："测试我的"

我认为我以前看到过这个问题，但在这里找不到相关建议。MS在IDictionary接口上有一个TryGetValue函数，但它返回一个布尔值，并在out参数中给出该值，因此在这里提供一个更简单、更清晰的实现：

public static TVal GetValueOrDefault<TKey, TVal>(this IDictionary<TKey, TVal> d, TKey key) {
  if (d.ContainsKey(key))
    return d[key];
  return default(TVal);
}

这是另一个控件扩展，我一直在使用，但不知道之前是否已发布在此处。

public static class ControlExtensions
{
    public static void DoubleBuffer(this Control control) 
    {
        // https://dev59.com/yXVD5IYBdhLWcg3wI36L#77233
        // Taxes: Remote Desktop Connection and painting: http://blogs.msdn.com/oldnewthing/archive/2006/01/03/508694.aspx

        if (System.Windows.Forms.SystemInformation.TerminalServerSession) return;
        System.Reflection.PropertyInfo dbProp = typeof(System.Windows.Forms.Control).GetProperty("DoubleBuffered", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
        dbProp.SetValue(control, true, null);
    }
}

使用方法：

this.someControl.DoubleBuffer();

我实现了一个扩展方法包（可在http://foop.codeplex.com/上获得），其中我经常使用的一些方法包括：

// the most beloved extension method for me is Pipe:
<%= variable.Pipe(x => this.SomeFunction(x)).Pipe(y =>
{
    ...;
    return this.SomeOtherFunction(y);
}) %>

var d = 28.December(2009); // some extension methods for creating DateTime
DateTime justDatePart = d.JustDate();
TimeSpan justTimePart = d.JustTime();
var nextTime = d.Add(5.Hours());

using(StreamReader reader = new StreamReader("lines-of-data-file-for-example")) {
    ...
    // for reading streams line by line and usable in LINQ
    var query = from line in reader.Lines(); 
                where line.Contains(_today)
                select new { Parts = PartsOf(line), Time = _now };
}

500.Sleep();

XmlSerialize and XmlDeserialize

IsNull and IsNotNull

IfTrue, IfFalse and Iff:
true.IfTrue(() => Console.WriteLine("it is true then!");

IfNull and IfNotNull

在我所有的项目中，我都会加入两个小东西（有些人可能觉得它们很傻），它们是：

public static bool IsNull(this object o){
  return o == null;
}

并且

public static bool IsNullOrEmpty(this string s){
  return string.IsNullOrEmpty(s);
}

这让我的代码更加流畅。

if (myClassInstance.IsNull()) //... do something

if (myString.IsNullOrEmpty()) //... do something

我认为这些会成为非常好的扩展属性；如果我们有了那些的话。

将字符串的长度缩短为toLength，并在缩短后的字符串末尾添加一个附加字符串以表示该字符串已被缩短（默认为...）。

public static string Shorten(this string str, int toLength, string cutOffReplacement = " ...")
{
    if (string.IsNullOrEmpty(str) || str.Length <= toLength)
        return str;
    else
        return str.Remove(toLength) + cutOffReplacement;
}